The specific aims of this proposal are to: (1) investigate the chemical structures, presence in vivo, and biological significance of DNA adducts formed from the carcinogens N-nitrosopyrrolidine, N-nitrosomorpholine, N-nitrosodiethanolamine, N-nitrosopiperidine, and N,N-dinitrosopiperazine. Our hypothesis is that the cyclic 1,N2-deoxyguanosine adducts and related adducts formed by these nitrosamines are involved in the initiation of the carcinogenic process. These studies will be carried out by reacting model compounds with DNA and its bases, characterizing the adducts, and measuring their initial levels and persistence in target and non-target tissues; (2) test our hypothesis that N-nitroso-2-hydroxymorpholine is a proximate or ultimate carcinogen of N-nitrosodiethanolamine by carrying out a comparative bioassay in rats; (3) investigate the in vivo formation of N-nitrosomorpholine or N,N-dinitrosopiperazine in humans treated with pharmaceuticals containing their precursors by using a sensitive new method for detection of their metabolites in urine; (4) investigate the role of glutathione conjugation in the metabolism of N-nitrosopyrrolidine and N-nitrosomorpholine by characterizing the products formed upon reaction of the appropriate model compounds with N-acetylcysteine or glutathione and assessing the formation of these products in vitro and in vivo. The research being carried out in this program is designed to answer fundamental questions on the mechanisms of metabolic activation and detoxification of a group of environmentally prevalent carcinogenic nitrosamines. Our goal is to develop practical strategies for cancer prevention based on the knowledge gained in these studies.